Ramjet for a supersonic and hypersonic aircraft

ABSTRACT

According to the invention, the wall ( 5 ) is mounted movably as one so as to be able to slide longitudinally in translation, bringing the joint line ( 14 ) closer to the fuel injector ( 9 ) so as progressively to modify the geometries of the oxidant inlet ( 16 ) and of the combustion chamber ( 15 ), said geometries passing progressively from a first state (I) in which, for a Mach number lying between 1.5 and 3, said oxidant inlet ( 16 ) constricts said oxidant flow only slightly and the combustion chamber ( 15 ) is long and divergent, to a second state (III) in which, for a Mach number lying between 8 and 12, said oxidant inlet ( 16 ) strongly constricts said oxidant flow and said combustion chamber ( 15 ) is shorter and exhibits a constant cross section.

[0001] The present invention relates to a ramjet for a supersonic andhypersonic aircraft, intended to operate over a wide range of speeds,especially between Mach 2 and Mach 8.

[0002] The design of such a ramjet, generally called compound ramjetbecause it possesses an extended operating domain, by virtue of thesuccession of a subsonic combustion phase and of a supersonic combustionphase, raises numerous difficulties both as regards the definition ofthe aerodynamic stream as well as the production of the structuredelimiting this stream.

[0003] Various techniques have been employed in order to attempt toovercome these difficulties. Among these techniques, one of the mostinteresting is that described by the document U.S. Pat. No. 5,727,382.

[0004] This document describes a ramjet including an elongate ramjetbody which consists of four walls opposite in pairs, which between themdelimit:

[0005] an inlet for a flow of oxidant,

[0006] a variable-geometry combustion chamber, which is provided with atleast one fuel injector and in which the oxidant/fuel mixing and thecombustion of said mixture are carried out, and

[0007] an exhaust nozzle, channeling the gases leaving said combustionchamber,

[0008] two of said opposite walls being flat and parallel to each other.

[0009] In this known ramjet, one of the other two opposite walls isproduced by the use of plates which are articulated one after the other,so as to be deformable. A system of actuators makes it possible to setup and maintain said deformable wall in the geometry desired as afunction of the conditions of flight. The advantage of such a controlleddeformable wall lies in the capability of precisely adapting theprogressive changes in the cross section of the combustion chamber alongthe length of the chamber to each flight condition, and in thepossibility of putting in place a geometric-nozzle neck suitable forsubsonic combustion. On the other hand, the practical production of sucha ramjet is complex and expensive, especially because of the changesbetween moving plates. Moreover, in order to be able to form asatisfactory subsonic combustion chamber, this ramjet has to include asupersonic combustion chamber which is a little too long, which to adegree limits the performance of said ramjet at high speed andcomplicates its cooling.

[0010] Furthermore, the document GB-2 222 635 describes a ramjet for asupersonic and hypersonic aircraft, including an elongate body whichconsists of:

[0011] two sidewalls, flat and parallel to each other;

[0012] a fixed upper wall, integral with said sidewalls and exhibiting,in profile, the rigid general shape of a V open at an obtuse angle, insuch a way that said upper wall includes a front flank and a rear flankwhich are inclined with respect to one another and linked by a ridgewhich is at least approximately orthogonal to said sidewalls; and

[0013] a lower wall mounted movably as one between said sidewalls so asto be able to slide longitudinally in translation, said lower wall alsofeaturing, in profile, the rigid general shape of a V open at an obtuseangle, but reversed with respect to that of said upper wall, said lowerwall thus including a front flank and a rear flank which are inclinedwith respect to one another and linked by a ridge at least approximatelyorthogonal to said sidewalls,

[0014] said walls of said body delimiting between them:

[0015] an inlet for a flow of oxidant;

[0016] a combustion chamber, which is provided with at least one fuelinjector and in which the oxidant/fuel mixing and the combustion of saidmixture are carried out; and

[0017] an exhaust nozzle, channeling the gases leaving said combustionchamber and formed between said rear flank of the upper wall and therear flank of the lower wall.

[0018] In this latter document, the sliding lower wall acts as a shockdiffuser.

[0019] The object of the present invention is such a ramjet with slidinglower wall making it possible to obtain an optimal combustion chamber,whether the combustion is subsonic or supersonic.

[0020] To that end, according to the invention, the ramjet with slidinglower wall, of the type reiterated above, is noteworthy in that:

[0021] said fuel injector is arranged in the vicinity of the ridge ofsaid upper wall;

[0022] said front flank of the lower wall includes:

[0023] at least one first face, in a general direction at leastsubstantially parallel to the rear flank of said upper wall and arrangedfacing said rear flank of said upper wall; and

[0024] at least one second face, linked securely to said first facealong a joint line at least approximately orthogonal to said sidewalls,said second face being inclined with respect to said first face in sucha way that, facing said upper wall, the assembly of said first face andof said second face is concave;

[0025] said ridge of the upper wall faces said second face of said lowerwall, while said joint line between said first and second faces liesopposite the rear flank of the upper wall, such that said second face isarranged with regard to said fuel injector with a part facing the rearflank of the upper wall and a part facing the front flank of said upperwall;

[0026] said combustion chamber is formed between, on the one hand, saidrear flank of said upper wall and, on the other hand, said first faceand the corresponding part of said second face of said lower wall;

[0027] said oxidant inlet is formed between the front flank of saidupper wall and the corresponding part of said second face of said lowerwall; and

[0028] the sliding of the lower wall brings said joint line between saidfirst and second faces closer to said fuel injector so as progressivelyto modify the geometries of said oxidant inlet and of said combustionchamber, said geometries passing progressively from a first state inwhich, for a Mach number lying between 1.5 and 3, said oxidant inletconstricts said oxidant flow only slightly and said combustion chamberis long and divergent, to a second state in which, for a Mach numberlying between 8 and 12, said oxidant inlet strongly constricts saidoxidant flow and said combustion chamber is shorter and exhibits aconstant cross section.

[0029] Hence, by virtue of the present invention, by simply employingthe linear or curvilinear translation of one of the walls of the ramjet,the progressive variation in the cross section of the combustion chamberand of the geometries of the oxidant inlet and of the nozzle areobtained, which makes it possible to match the ramjet to the conditionsof flight of the aircraft, so as to obtain the maximum performance fromit as regards either the thrust, or the specific impulse. To do this,the two walls of the ramjet, other than the two which are flat andparallel to each other, are profiled in such a way that said translationleads to very different cross section laws being imposed; an oxidant(air) inlet with a low degree of constriction associated with a long anddivergent combustion chamber equipped with a geometric-nozzle neck forthe low Mach numbers, and an air inlet with a high degree ofconstriction associated with a shorter combustion chamber with constantcross section for the high Mach numbers.

[0030] The implementation of the present invention therefore makes itpossible to dispense with the variable-geometry wall of the ramjet ofthe document U.S. Pat. No. 5,727,382, with its drawbacks which are thehinges for articulation of the plates, the plurality of actuators forthese plates, etc. In contrast, in the ramjet of the invention, a singleactuator is necessary in order to achieve said translation. Furthermore,it is possible to accept an incomplete leaktightness of said wall whichis movable in translation with said flat and parallel walls.

[0031] Said movable second wall is preferably shorter than said firstupper wall.

[0032] Furthermore, in order to form, with said second face, a markedinlet neck (minimum cross section) for the oxidant flow, the ridge ofsaid first wall exhibits the shape of a bevel.

[0033] The figures of the attached drawing will give a goodunderstanding of how the invention can be produced. In these figures,identical references designate similar elements.

[0034]FIG. 1 shows, in a diagrammatic view in perspective, with partialcutaway, an examplary embodiment of the ramjet in accordance with thepresent invention.

[0035]FIG. 2 is a diagrammatic view in transverse section along the lineII-II of FIG. 1.

[0036]FIG. 3 is a partial diagrammatic side view along the line III-IIIof FIG. 2.

[0037]FIG. 4 is a diagram, in diagrammatic longitudinal view,illustrating the main elements of the ramjet in accordance with thepresent invention.

[0038]FIG. 5 and FIG. 6 respectively illustrate the relative positionsof the main elements of said ramjet, at the front end and at the rearend thereof, for operation at Mach 3.

[0039]FIG. 7 and FIG. 8 correspond respectively to FIGS. 5 and 6, foroperation of the ramjet at Mach 6.

[0040]FIG. 9 and FIG. 10 correspond respectively to FIGS. 5 and 6, foroperation of the ramjet at Mach 8.

[0041]FIG. 11 is a diagram indicating an altimetric-trajectory example,as a function of the flight Mach number, for the ramjet in accordancewith the present invention.

[0042]FIG. 12 is a diagram indicating the specific impulse as a functionof the flight Mach number, for said ramjet.

[0043] The ramjet for an aircraft according to the invention illustratedby FIGS. 1 to 4 includes an elongate ramjet body 1 consisting of fourwalls 2 to 5, opposite in pairs. The two opposite sidewalls 2 and 3 areflat and parallel to each other.

[0044] The upper wall 4 is integral with the two sidewalls 2 and 3 andit exhibits a general, fixed shape, with a V-profile open at an obtuseangle. It includes a front flank 6 and a rear flank 7 which are inclinedwith respect to one another and linked by a beveled ridge 8. Asillustrated by the figures, the front flank 6 and rear flank 7 may, inpractice, each include facets which are slightly inclined with respectto one another.

[0045] Fuel injectors 9 are arranged in the vicinity of the ridge 8.

[0046] The lower wall 5, the length e of which is less than the length Lof the upper wall 4, also exhibits a general, fixed shape, with a Vprofile open at an obtuse angle. It is inverted with respect to theupper wall 4. It includes a front flank 11 and a rear flank 12 which areinclined with respect to one another and linked by a ridge 13.

[0047] The front flank 11 of the lower wall 5 includes a first face 11A,the general direction of which is at least substantially parallel to therear flank 7 of the upper wall 4, and which is arranged facing thislatter flank 7. The flank 11 further includes a second face 11B, linkedsecurely to said first face 11A along a joint line 14 and orthogonal tothe sidewalls 2 and 3. The second face 11B is inclined with respect tothe first face 11A so as to form a concavity facing the upper wall 4.

[0048] As can be seen clearly in FIG. 4 (drawn in a reference systemwith rectangular axes ox, oy and oz defined in FIG. 1 and in which theaxes ox and oz are respectively parallel to the length and to the heightof said ramjet):

[0049] the ridge 8 of the upper wall 4 is arranged facing the secondface 11B of the lower wall 5;

[0050] the joint line 14 and the ridge 13 of the lower wall 5 arearranged facing the rear flank 7 of the upper wall 4;

[0051] the first face 11A of the lower wall 5 lies entirely opposite therear flank 7 of the upper wall 4; and

[0052] the second face 11B of the lower wall 5 lies opposite theinjectors 9, the front part of said second face 11B being opposite thefront flank 6 of the upper wall 4, whereas the rear wall of this face11B is facing the rear flank 7 of the upper wall 4.

[0053] Hence, in the ramjet of FIGS. 1 to 4:

[0054] the combustion chamber 15 is formed between, on the one hand, therear flank 7 of the upper wall 4 and, on the other hand, the first face11A and the part of the second face 11B of the lower wall 5 which isopposite said rear flank 7;

[0055] the oxidant (air) inlet 16 is formed between the front flank 6 ofthe upper wall 4 and the part of the second face 11B of the lower wall 5facing said front flank 6; and

[0056] the exhaust nozzle 17 is formed between the rear flank 7 of theupper wall 4 and the rear flank 12 of the lower wall 5.

[0057] Furthermore, the lower wall 5 of the ramjet 2 is mounted movably,in its entirety, between said sidewalls 2 and 3, so as to be able toslide longitudinally in translation.

[0058] In FIG. 1, which is merely a diagrammatic illustration:

[0059] the sliding and guidance means have been represented in the formof external jacks 18, 19 and of spindles 20, 21 sliding in ramps 22,cutout into the sidewalls 2 and 3. Thus, the jacks 18, 19 can push thespindles 20, 21 which, guided by the ramps 22, slide in order todisplace the lower wall 5 with respect to the upper wall 4 and to thesidewalls 2 and 3. Needless to say, such sliding and guidance means areonly diagrammatic, and they could advantageously be replaced by motormeans housed at least partly within said lower wall 5;

[0060] the ramp 22 represented by a solid line in FIG. 3 is rectilinear,but, needless to say, it could be curvilinear, as is illustrated indashed lines; and

[0061] the joints between the lower wall 5 and the sidewalls 2 and 3have not been represented, nor the sealing system as regards the ramp22.

[0062] Whatever the practical embodiment of said sliding and guidancemeans, it can easily be envisaged that they make it possible to displacesaid lower wall 5 so as to bring the joint line 14 progressively closerin translation to the injectors 9, so as progressively to modify thegeometries of the oxidant inlet 16 and of the combustion chamber 15.

[0063] In FIG. 4, three successive positions of the lower wall 5 withrespect to the other walls 2, 3 and 4 have been sketched, thesesuccessive positions being designated respectively by the references I,II and III, and corresponding, for example, to different flight Machvalues Mf respectively.

[0064] In position I, illustrated in further detail in FIGS. 5 and 6(FIG. 5 being to a scale twice that of FIG. 6) and corresponding to arelatively low flight Mach Mf equal to 3, it can be seen (FIG. 5) thatthe oxidant inlet 16 is relatively slightly convergent and imposes onlya small degree of constriction on the oxidant flow, while (FIG. 6) thecombustion chamber 15 is however long and divergent.

[0065] In position II (see FIGS. 7 and 8, with FIG. 7 to a scale twicethat of FIG. 8) corresponding to an intermediate flight Mach Mf of 6 itcan be seen that, by comparison with position I, the oxidant inlet 16 ismore convergent and constricts the oxidant flow (FIG. 7) more strongly,while the combustion chamber 15 is less long and less divergent.

[0066] Finally, in position III (see FIGS. 9 and 10, with FIG. 9 to ascale twice that of FIG. 10) corresponding to a flight Mach Mf of a highvalue equal to 8, the oxidant inlet is strongly convergent and imposes ahigh degree of constriction on the oxidant flow and, simultaneously, thecombustion chamber is short and features a constant cross section overits entire length.

[0067] Hence it is seen that, by virtue of the present invention, it ispossible progressively to modify the geometries of the oxidant inlet 16and of the combustion chamber 15 in step with the increase in the valueof the flight Mach Mf so as to cause the geometries to changeprogressively from a first state, which is appropriate for a lowsupersonic flight Mach (Mach 1.5 to 3) and in which the oxidant inletonly slightly constricts the oxidant flow, and the combustion chamber islong and divergent, to a second state, which is appropriate to a highsupersonic flight Mach (Mach 8 to 12) and in which said oxidant inletstrongly constricts the oxidant flow and said combustion chamber isshort with a constant cross section.

[0068] The curve 23 of FIG. 11 illustrates an example of a variation inthe altitude H (in km) of the ramjet as a function of the flight Machnumber Mf. On this curve 23 have been indicated the operating pointscorresponding to the states I, II and III detailed above.

[0069] Likewise, on the curve 24 of FIG. 12, illustrating the variationin the specific impulse Isp (in m/s) as a function of the flight Machnumber Mf, the points corresponding to said states I, II and III havebeen put in place.

1. A ramjet for a supersonic and hypersonic aircraft, including anelongate body which consists of: two sidewalls, flat and parallel toeach other; a fixed upper wall, integral with said sidewalls andexhibiting, in profile, the rigid general shape of a V open at an obtuseangle, in such a way that said upper wall includes a front flank and arear flank which are inclined with respect to one another and linked bya ridge which is at least approximately orthogonal to said sidewalls;and a lower wall mounted movably as one between said sidewalls so as tobe able to slide longitudinally in translation, said lower wall alsofeaturing, in profile, the rigid general shape of a V open at an obtuseangle, but reversed with respect to that of said upper wall, said lowerwall thus including a front flank and a rear flank which are inclinedwith respect to one another and linked by a ridge at least approximatelyorthogonal to said sidewalls, said walls of said body delimiting betweenthem: an inlet for a flow of oxidant; a combustion chamber, which isprovided with at least one fuel injector and in which the oxidant/fuelmixing and the combustion of said mixture are carried out; and anexhaust nozzle, channeling the gases leaving said combustion chamber andformed between said rear flank of the upper wall and the rear flank ofthe lower wall, wherein: said fuel injector is arranged in the vicinityof the ridge of said upper wall; said front flank of the lower wallincludes: at least one first face, in a general direction at leastsubstantially parallel to the rear flank of said upper wall and arrangedfacing said rear flank of said upper wall; and at least one second face,linked securely to said first face along a joint line at leastapproximately orthogonal to said sidewalls, said second face beinginclined with respect to said first face in such a way that, facing saidupper wall, the assembly of said first face and of said second face isconcave; said ridge of the upper wall faces said second face of saidlower wall, while said joint line between said first and second faceslies opposite the rear flank of the upper wall, such that said secondface is arranged with regard to said fuel injector with a part facingthe rear flank of the upper wall and a part facing the front flank ofsaid upper wall; said combustion chamber is formed between, on the onehand, said rear flank of said upper wall and, on the other hand, saidfirst face and the corresponding part of said second face of said lowerwall; said oxidant inlet is formed between the front flank of said upperwall and the corresponding part of said second face of said lower wall;and the sliding of the lower wall brings said joint line between saidfirst and second faces closer to said fuel injector so as progressivelyto modify the geometries of said oxidant inlet and of said combustionchamber, said geometries passing progressively from a first state inwhich, for a Mach number lying between 1.5 and 3, said oxidant inletconstricts said oxidant flow only slightly and said combustion chamberis long and divergent, to a second state in which, for a Mach numberlying between 8 and 12, said oxidant inlet strongly constricts saidoxidant flow and said combustion chamber is shorter and exhibits aconstant cross section.
 2. The ramjet as claimed in claim 1, wherein thetranslation of said lower wall is rectilinear.
 3. The ramjet as claimedin claim 1, wherein the translation of said lower wall is curvilinear.4. The ramjet as claimed in claim 1, wherein the said lower wall isshorter than said upper wall.
 5. The ramjet as claimed in claim 1,wherein the ridge of said upper wall exhibits the shape of a bevel soas, with said second face, to define a minimum inlet cross section forthe flow of oxidant.